Thermal self-crosslink after etching for regulated preparation of Ti3C2 type MXene membrane and its preliminary gas separation

We present an innovative methodology for the synthesis of MXene membranes through a dual-stage process involving etching and subsequent thermal self-crosslinking. A molar ratio of 1 (Al3+):9 (F-) using HCl/LiF was employed to convert raw Ti3AlC2 (MAX phase) into MXene within 48 hours at 40 °C. This procedure predominantly yielded monolayers distinguished by diameters exceeding 500 nm, elevated crystallinity and a high overall yield. Advanced characterization techniques, including FESEM, TEM, HRTEM, AFM, XPS, and FTIR, were utilized. Instrumental analysis confirmed the formation of MXene exhibiting a single-flake morphology with diameters exceeding 500 nm. These monolayers were intact and continuous, with smooth peripheries and a uniform thickness of 2.1 nm. The surfaces were predominantly composed of carbon (C), oxygen (O), and titanium (Ti) atoms, interconnected by chemical bonds such as C−Ti−O, C−Ti−OH, C−C, C−O, and Ti−O. In the subsequent phase, vacuum filtration facilitated the assembly of a self-supporting MXene membrane. Thermal treatment at 170 °C for 30 hours resulted in the reinforcement of C-Ti-O bonds within the nanosheets, increasing their prevalence to 43.14% and 19.47%, respectively. This thermal regulation reduced the interlayer d-spacing from 4.33 to 3.54 Å, which significantly improved the gas separation efficiency beyond the Knudsen diffusion limit, as demonstrated by the value exceeding 23.0.